The present disclosure generally relates to processing of materials for growth of crystals. More particularly, the present disclosure provides methods for obtaining a gallium-containing nitride crystal by an ammonothermal technique, including ammonobasic or ammonoacidic techniques, but there can be others. In certain embodiments, the present disclosure provides an apparatus for large scale processing of nitride crystals, but it would be recognized that other crystals and materials may also be processed. Such crystals and materials include, for example, GaN, AlN, InN, InGaN, AlGaN, AlInN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates may be used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation devices, photodetectors, integrated circuits, power electronics, and transistors, among other devices.
Gallium nitride containing crystalline materials serve as a starting point for manufacture of conventional optoelectronic devices, such as blue light emitting diodes and lasers. Such optoelectronic devices have been commonly manufactured on sapphire or silicon carbide substrates that differ in composition from the deposited nitride layers. In conventional Metal-Organic Chemical Vapor Deposition (MOCVD) methods, deposition of GaN is performed from ammonia and organometallic compounds in the gas phase. Although successful, conventional growth rates make it difficult to provide a bulk layer of GaN material. Additionally, dislocation densities are also high and lead to poor optoelectronic device performance.
Other techniques have been proposed for obtaining bulk monocrystalline gallium nitride. Such techniques include epitaxial deposition employing halides and hydrides in a vapor phase, e.g., Hydride Vapor Phase Epitaxy (HVPE) (Motoku et al., “Growth and characterization of freestanding GaN substrates,” Journal of Crystal Growth 237-239, 912 (2002)). Unfortunately, drawbacks exist with HVPE techniques. In some cases, the quality of the bulk monocrystalline gallium nitride is not generally sufficient for high quality laser diodes because of issues with dislocation density, stress, and the like. In addition, scale-up of HVPE is difficult and costs tend to be high, particularly for manufacturing of semipolar boules and wafers.
Techniques using supercritical ammonia have been proposed. Peters has described the ammonothermal synthesis of aluminum nitride (J. Cryst. Growth 104, 411-418 (1990)). Dwilinski et al. have shown that it is possible to obtain fine-crystalline gallium nitride by a synthesis from gallium and ammonia, provided that the latter contains alkali metal amides (KNH2 or LiNH2). These and other techniques have been described in “AMMONO method of BN, AlN, and GaN synthesis and crystal growth,” Proc. EGW-3, Warsaw, Jun. 22-24, 1998, MRS Internet Journal of Nitride Semiconductor Research, “Crystal growth of gallium nitride in supercritical ammonia,” Kolis et al., J. Cryst. Growth 222, 431-434 (2001), and Kolis et al., Mat. Res. Soc. Symp. Proc. Vol. 495, 367-372 (1998). However, using these supercritical ammonia processes, wide scale production of bulk monocrystalline was not achieved, particularly for semipolar boules and wafers.
Dwilinski, in U.S. Pat. Nos. 6,656,615 and 7,335,262, and D'Evelyn, in U.S. Pat. Nos. 7,078,731 and 7,101,433, disclose apparatus and methods for conventional ammonothermal crystal growth of GaN. These methods are useful for growth of relatively small GaN crystals. Unfortunately, such methods have limitations for large scale manufacturing. The conventional apparatus with an inner diameter of 40 mm is useful for growing smaller diameter GaN crystals but is not suitable for large scale growth of GaN boules. Additionally, conventional suspension of seed crystals using wires passing through single laser-drilled holes may be adequate for small crystals but is not amenable to large scale manufacturing. Other limitations may also exist.
From the above, it can be appreciated that improved techniques for large scale GaN crystal growth are desired, particularly for semipolar boules and wafers.